Nuke Anything Enhanced - Firefox Addon - Allows you to hide almost anything via context menu 'Remove Object' or 'Remove Selection' with possibility of multiple undo of 'Remove Object'. You can also make a selection and chose "Remove everything else" to clear the page and only leave the selected text.
Once you decide what you want to Remove, Right click on it or select it, then select "Remove this Object" from the menu.

The effect of this extension is temporary, which is useful before printing a page, you can use another extension, 'Remove It Permanently' if you want your removed objects to be remembered.